**Question:** True about rigor mortis - a) First appear in chin; b) It last 18-36 hours in summer; c) Seen immediately after death; d) It disappears in the sequence as it appears; e) It last 24-48 hours in winter

**Core Concept:** Rigor mortis is a post-mortem phenomenon that occurs due to the release of calcium ions from muscle cells, leading to muscle contraction and stiffness. This process is influenced by temperature, with warmer temperatures accelerating rigor mortis progression.

**Why the Correct Answer is Right:**

Option A (First appear in chin) is not entirely accurate as rigor mortis initially affects the jaw muscles, but it also spreads to other facial muscles and eventually the entire body. Option B (It last 18-36 hours in summer) is partially correct, as rigor mortis generally lasts longer in cooler temperatures (winter) and shorter in warmer temperatures (summer).

Option C (Seen immediately after death) is incorrect as rigor mortis may not be immediately noticeable due to the gradual progression of the process. Option D (It disappears in the sequence as it appears) is incorrect since rigor mortis affects the entire body simultaneously.

Option E (It last 24-48 hours in winter) is partially correct, as rigor mortis lasts longer in cooler temperatures. However, it does not account for the progression of rigor mortis in the facial muscles and other body parts.

**Why Each Wrong Option is Incorrect:**

Option A (First appear in chin) is incorrect because rigor mortis initially affects the jaw muscles but spreads to other facial muscles and eventually the entire body.

Option C (Seen immediately after death) is incorrect as rigor mortis may not be immediately noticeable due to the gradual progression of the process.

Option D (It disappears in the sequence as it appears) is incorrect because rigor mortis affects the entire body simultaneously, not in a sequential manner.

Option E (It last 24-48 hours in winter) is partially correct but does not account for the progression of rigor mortis in facial muscles and other body parts.

**Core Concept:** Rigor mortis is a post-mortem phenomenon caused by the release of calcium ions from the sarcoplasmic reticulum of muscle cells. As the body cools after death, calcium ions accumulate in the sarcoplasm, leading to muscle contraction and stiffness.

**Why the Correct Answer is Right:**

Option E (It lasts for 24-48 hours) is partially correct as rigor mortis duration can vary depending on temperature. In cooler temperatures (winter), rigor mortis lasts longer due to reduced muscle activity. However, this option does not address the progression of rigor mortis in facial muscles and other body parts.

**Why Each Wrong Option is Incorrect:**

Option A (First appears in the chin) is incorrect because rigor mortis initially affects the jaw muscles but spreads to other facial muscles and the entire body.